1. Field of the Invention
The present invention relates to measurement devices and, more particularly, to a caliper measurement assembly utilizing an attachment member specifically adapted for precise manual measurements of a known curvature.
2. History of the Prior Art
Measurement systems of varying degrees of accuracy date back into technological antiquity. Such measuring devices often utilize simple indicia indicating the distance measured. These devices include simple rulers and tape measures as well as more mechanically complex gauges and calipers of conventional design. Machining precision and engineering creativity have produced a wide variety of precision instruments capable of manually measuring minute distances.
The availability of precision measurement devices has, in turn, revolutionized the machining industry and the mechanical measuring art itself by providing simple, reliable devices that are capable of precision measurements on a relatively small scale. The magnitude of measurable distances has decreased as machining precision has increased. Several prior art patents reflect this progress. An early version of a gauge adapted for measuring the depth of a hole and the length or width of an article is seen in U.S. Pat. No. 597,335 which issued in 1898 entitled "Micrometer Depth Gage." The device set forth and shown therein incorporates a screw-thread adjustment member with preselected indicia showing the distance of movement of the adjustment member relative to a flat base which is used to position the device for measurement. Measurements are manually made by utilizing the incremental movement of the screw-thread mounting and the indicia formed upon the body relative thereto.
Another example of measurement technology from the last century is seen in U.S. Pat. No. 490,860, an earlier version of a precision "depth gauge" which was patented in 1893. This device was said to be capable of measuring the diameter of holes as well as the depths of different parts of a cavity of unequal depth by utilizing a tapered spindle which extended from a flat positioning surface. Again, preselected indicia were provided on the body of the depth gauge for visual observation of the measured diameter and depth of the hole by the user.
U.S. Pat. No. 2,611,187 was issued in 1952 for a "Keyway Location Gauge." In this particular reference, it is seen that specific adaptations of the earlier depth gauge were utilized for measuring the relationship between the centerline of a keyway with respect to the axis of a shaft in which the keyway was located. The gauge of this particular invention was to be constructed with "V-shaped" blocks forming an angulated positioning surface. The "V" blocks were adapted to engage a round shaft so that the apex of the "V" would be precisely parallel with the axis of the shaft for purposes of measurement. An extendable element fit into the slot, and preselected indicia measured any misalignment between the axis of the slot and the axis of the shaft.
More conventional depth measurement devices also include the assembly shown in U.S. Pat. No. 4,631,831. This 1986 patent teaches a tread depth probe for manually measuring the depth of a tread groove in a tire from a generally planar position on the surface of a tire. This particular device then indicates the result of that measurement on a computerized display screen. As was common with earlier vintage depth gauges, a probe is extended from a flat surface of the gauge into the region to be measured, and the displacement of the probe is precisely measured and displayed to the user.
It may be seen that the measurement of various depths, and distances related thereto, is easily determined by the use of gauges and calipers once a positioning plane, or "base line", is provided. In the prior art discussed above, the base line is either a planar region or is formed from angulated blocks for "centering" upon the surface to be measured. While effective in centering items on a shaft and/or measuring the diameter or depth of holes or cavities in a flat surface, none of the prior art gauges are specifically adapted for the precision measurement of deviations from the curvature of a round surface. The manual measurement of the preciseness of the curvature of a round surface, however, may often be more critical an operation than the measurement of a flat surface. For example, in mechanisms utilizing round parts rotating at high speeds, a critical measurement is whether the surface of such parts is "out of round". A precise manual measurement of this nature would be difficult, if not impossible, with prior art gauges and calipers of the type discussed above, thereby necessitating the use of a more complex and expensive measurement system. More complex devices, such as optical systems, are capable of such precision measurements, but these are often cost prohibitive and time-consuming.
In the air transportation industry, the demands for economical, precision measurements within close tolerances are well known. A multitude of extremely precise measurements must be taken frequently upon a myriad of aircraft parts in order to maintain aircraft performance and safety margins. For example, safety regulations require that the surfaces of certain round areas be kept within precisely specified tolerance limits. The usual means for measuring such surfaces is with conventional measuring devices of the type discussed above. Using such devices, however, it is difficult to obtain repeated accurate measurements of objects having a small radius of curvature which extends over a large area. Such areas may include shafts and the outer rim of aircraft wheel structures, where there is biaxial curvature. One axis of wheel rim curvature is that of the wheel radius itself (often measured in feet), while a second axis of curvature is that of the lip or rim of the wheel, often measured in inches. When attempting to measure such regions, it is difficult to establish a zero reference point (base line) for the measurement probe, and even more difficult to maintain the measurement probe in the proper biaxial orientation during manual measurement operations. This task becomes extremely troublesome when the operation must be consistently repeated at multiple points around the rim of the wheel.
The present invention overcomes the problems of the prior art by providing a measuring device attachment member which may be specifically configured for engaging regions of known curvature of certain parts. The attachment member includes a surface having a mating configuration to that of the part being measured. In this manner, the measuring device can abuttingly engage the surface being measured in general conformity therewith. Thus a base line is easily established, and the probe can be readily calibrated for a zero-deviation reading ("zeroed out") at the initial measurement position. Manual stabilization of the measuring device during measurement operations is also greatly enhanced, as the proper biaxial orientation is more easily maintained. Additionally, multiple measurements may be accurately and consistently repeated, for example, around the entire circumference of a wheel or along the entire length of a shaft for the detection of chips, gouges and other "out of round" regions upon the engaged surface. The attachment member may also be incorporated in automated systems, as set forth herein.